Arc testing device

ABSTRACT

A testing device for switching a pair of electrical contacts to draw an arc at a precisely controlled phase angle and for a precisely controlled time interval across a high voltage AC source. A phase sensor detects a selected phase angle of the source and starts a time delay circuit which measures a selected delay interval. At the end of that interval a triggering circuit turns on a three phase power output stage which energizes a pair of opposed synchronous linear actuators to switch the contacts, thus initiating an arc at a precisely controlled phase angle. Control of the actuator drive voltage enables the contact transport speed to be controlled, which in turn governs arc duration. A protective circuit determines when the arc tester starts and stops operation.

United States Patent Russakoff et al. Sept. 26, 1972 [s41 ARC TESTING DEVICE Primary ExaminerEli Lieberman [72] Inventors: Robert S. Russakoi'f, Weston, Conn.; Assam! Exammer Marvm Nussbaum Qarlo Brlmo DeLuca, Monroe, Conn. Henry Schenker, Fairfield, Conn.;

Alfred -L. Henchcliffe, Trumbull,

Com; Pse 911 3 9 walk, Conn. Assignee; Burndef Corporation Attorneyl-loward S. Reiter [5 7] ABSTRACT A testing device for switching a pair of electrical contacts to draw an arc at a precisely controlled phase angle and for a precisely controlled time interval across a high voltage AC source. A phase sensor de- A [-22] Filed: 1970 tects a selected phase angle of the source and starts a [21] APPL 02 233 time delay circuit which measures a selected delay interval. At the'end of that interval a triggering circuit turns on a three phase power output stage which ener- [52] US. Cl ..315/l94, 315/357 gizes a pair of opposed Synchronous linear actuators [5i] lilt- Cl. H051) to it h th contacts th i iti ti an are t a Field of Search 315/194, 247, 327, 357, 199; precisely controlled phase angle. Control of the actua- 324/28 tor drive voltage enables the contact transport speed to be controlled, which in turn governs arc duration. [56] References Cited A protective circuit determines when the arc tester t t d l. I UNITED STATES PATENTS 8 ar S P 3,206,642 9/1965 Farvis ..307/l33 x 3 5 Dmwmg 102 403 408 A f 402 4 2 w 405 M F gm $22 I M P'A'TE'N'TEB SW26 m2 SHEEI 2 BF 3 INVENTOR.

E X AW 8 W n r. R l 0 Em .rcM. T C. .A n A WR D W K AN a m UC R RH Y B PATENTEDszrzs m2 SHEET 3 BF 3 malts.

BY DWILUAMS @Q lk 1 ARC TESTING DEVICE FIELD OF THE INVENTION The invention relates generally to test equipment for the electrical power industry, and particularly concerns a device for striking high power arcs of known duration and at known phase angles.

THE PRIOR ART The problem of arcing is an ever-present one for the electrical power industry. Arcs are unavoidably struck in the connecting or disconnecting of live circuits under a variety of conditions; for example when a new service is connected to a live circuit, when a protective breaker trips out, or a service man must pull a line under emergency conditions in the field. In order to deal with this problem, the power companies find it desirable to do research into the characteristics of electrical arcs, particularly those which occur at relatively high voltage levels, such as KV. But it is not enough simply to strike anarc and observe it consequences, without knowing the duration of the arc and the precise phase angle of the electrical source when the arc was struck. Accordingly there is a need for test equipment which will permit high voltage arcs to be struck in the laboratory for precise times and at precisely controlled electrical phase angles.

There is presently test equipment for accomplishing this by electrically controlling the tum-on and tum-off time of an are between a pair of immobile contacts. But such equipment has proved unsatisfactory, because the use of immobile contacts does not adequately reflect the electrical or mechanical situation actually encountered when contacts are made or broken in the field.

At the present time the equipment which is available for switching contacts mechanically on demand in high voltage circuits is rather crude, simply involving the manual making or breaking of a circuit by a human operator equipped with a wooden pole. There are circuit breakers which employ sophisticated synchronous linear actuators to trip a circuit, but this type of device is designed to respond to a fault at any time and under any conditions, and thus does not have any provision for recognizing phase angle or controlling arc duration.

THE INVENTION This invention provides a sophisticated piece of test equipment which permits high voltage arcs to be made or drawn deliberately at a controlled time, so that the arc effects can be studied as a function of arc duration and of the phase angle of the electrical source. The device is set to be triggered at a selected phase angle of the electrical source by employing a phase sensing circuit and a tuneable delay circuit to trigger a switching stage. The latter turns on a power output stage to drive linear actuator means which open or close a pair of contacts connected across that same source. The moment when contact transport begins is thus precisely controlled as a function of phase angle. Then, by controlling the linear actuator drive voltage, the length of time required for the contacts to travel to the arc inception point, and subsequently to the arc termination point, is determined; so that arc inception can be made to occur at a controlled phase angle, and the arc can be made to endure for a controlled time interval thereafter. In order to prevent burning out of the linear actuator coils through prolonged operation, a protective circuit is provided to turn the test device on and off at appropriate times.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a functional block diagram of the electrical circuit of an are testing device in accordance with this invention.

FIG. 2 is a schematic circuit diagram of the same device.

FIG. 3 is a diagrammatic illustration of a pair of three phase synchronous linear actuators arranged in opposed relation for opening a pair of electrical contacts.

FIG. 4 is a schematic circuit diagram of the power connections to the linear actuator devices of FIG. 3.

FIG. 5 is a schematic diagram of a protective circuit for use with that of FIG. 2.

The same reference characters refer to the same elements throughout the several views of the drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The objective of a test program carried out with the apparatus of this invention is to determine the effects of high voltage arcs drawn when circuits are made or broken for various known intervals at various known phase angles of a high voltage AC source. Experiments of this nature are best powered by a separate test generator 100, to avoid imposing electrical shocks upon the local power distribution network when arcs are drawn. Thus the generator might be a piece of rotating machinery of laboratory size, generating a Y- connected three phase output at voltage levels in the neighborhood of 10 KV. A pair of contacts 102 are connected across the generator 100, and are opened or closed in order to strike the arc by actuators 104 which respond to three phase energization delivered over leads 105 by a Variac type of control circuit 107, leads 103, and a triac circuit 106. The circuit 106 preferably draws its power from the same generator 100 over three phase leads 108 as shown. (If the triacs were energized from the local power distribution network or any other source beside the one which energizes the arcing contacts 102, the generator phase and frequency would have to be identical or precisely known in relation to that of the triac supply, or the voltage threshold switching characteristics of the triac devices would introduce a large uncertainty into the control of the time at which contact transport begins). In the circuit illustrated, one side of the triac circuit 106 is connected to ground over a lead 110. The center point of the generator 100 is also grounded.

In order to start the linear actuators 104 at a precise phase angle of the arc source generator 100, a phase sensor circuit 112 is connected by leads 109 and 111 to the same phase of the generator output (i.e. to the same one of the leads 108) as the contacts 102. The triac circuit 106, which provides power to the linear actuators 104, is turned on by a signal arriving over a lead 115 from a trigger switch circuit 114, which in turn responds to a signal arriving over a lead 117 at the end of a time interval measured by a tuneable time delay circuit 116. The time interval measured by circuit 116 is adjustable, and starts when the phase angle detection output of the circuit 112 is received over a lead 113.

The purpose of the adjustable time delay interval introduced by circuit 116 is to compensate for delays introduced by friction and other mechanical resistances, and in particular by the inertia of the linear actuators 104, and also for certain additional delays and limitations inherent in the operation of the electrical circuits. Thus if the phase sensor circuit 112 senses a predetermined phase angle during one cycle of the generator 100; and if the sensing threshold of the circuit 1 12 plus all the combined mechanical delays and the electrical delays introduced by the response times of circuits 1 12, 116, 114 and 106 make it impossible thereafter to switch the contacts 102 in time for the arc to occur at the desired phase angle of that cycle; then the tuneable time delay circuit 116 is adjusted for a delay period of somewhat more than one cycle of the generator 100, so that the contacts 102 are switched at the desired phase angle of the following cycle.

As seen in the detailed circuit diagram of FIG. 2, the phase sensing input lead 111 is connected through a manual on-off switch 200, an isolating transformer 202, and a protective fuse 204 to the input of the phase sensor circuit 112. The phase sensor comprises a diode 206 which provides half-wave rectification of the 60 cycle AC input drawn from leads 111,109 and 108. The half-waverectified 60 cycle waveform is then applied through 'a current limiting resistor 208 to the anode of a silicon controlled rectifier 210. The voltage across the SCR 210 is regulated by a Zener diode 212 which is returned to the secondary of transformer 202 over a lead 214.

SCR 210 is in series with a load resistor 216, and its gate is connected to the adjustable tap in a voltage divider comprising a resistance 218 and a potentiometer 220. At some'point during the rising portion of a positive half-wave of the rectified 60 cycle input, i.e. between and 90 the gate voltage will rise to the fixed threshold which triggers the SCR 210. Adjustment of the potentiometer 220 determines the particular phase angle of the 60 cycle input at which that SCR triggering voltage occurs.

The output wave form developed across the SCR load resistor 216 is a positive-going square wave which begins at the phase angle when triggering of the SCR 210 occurs, and ends at 180 of the 60 cycle waveform when the input voltage to circuit 112 drops to zero, thus extinguishing SCR 210. This square wave output voltage is picked off by a lead 222 and applied to a differentiating circuit comprising a series capacitance 224 and shunt resistance 226. The output of the differentiating network 224, 226 is a positive spike coinciding with each leading edge of the square wave developed across resistor 216, and a negative spike coinciding with each trailing edge of that square wave. The negative spikes are not used, but the positive spikes represent markers coinciding with the particular phase angle of the 60 cycle input which the phase sensor circuitl 12 is adjusted to detect.

The potentiometer 220 adjusts the detected phase angle within certain limits. In a practical embodiment constructed according to the circuit of FIG. 2, the range of phase sensing which can be achieved is from a lower limit of approximately 15 to an upper limit of about 89, the exact cut-offs depending upon the gate threshold voltage of the SCR 210. If it is desired to strike the are at some phase angle which, with due regard for the electrical and mechanical delays involved,

requires sensing of a phase angle below the lower limit or above the upper limit of the available range, it is necessary to sense some other phase angle which is in that range and then wait a measured time interval of more than one cycle until the desired arcing phase angle occurs in the following cycle. It is for this purpose, among others, that the tuneable time delay circuit 116 is provided. That circuit is triggered by the phase sensor 112 at the selected phase angle in the available range from 15 to 89, and then measures a delay interval which lasts until some other phase angle of the following cycle. The range of adjustment of the delay circuit 116 is great enough to terminate the delay interval anywhere from 0 to 360 of the following cycle.

Another function served by the delay circuit 116 is that it also compensates for the delays resulting from inertia and mechanical resistance when the electrical contacts 102 are transported, and the additional delays due to the tum-on time of the various electrical components in the schematic circuit diagram of FIG. 2. The time delay introducedby the circuit 116 is made long enough so that the response time of all circuit components plus the mechanical delays plus the time delay of circuit 116 itself, when added together, are sufficient to shift the arc to the desired phase angle of the following cycle. v

The series of spikes across resistor 226, which represents the output of the phase sensor circuit 112, is applied through a normally open, relay-closed switch 230 and over a lead 113 to an RF filter comprising a shunt resistance 232 and capacitance 234. The filter output is applied through a current limiting resistance 236 to the gate of an SCR 238, the anode-cathode circuit of which is in series with a normally closed, relayopened switch 240, a normally closed, manually opened switch 242, and a battery or other. DC source 244. The positive spike from the phase sensor circuit 112, which indicates the turning on of SCR 210 at a selected phase angle of AC source 100, turns on the SCR 238 of delay circuit 1 16. Battery 244 is connected through current limiting resistors 246 and 248 to power a unijunction transistor 250. The UJT return circuit back to battery 244 through load resistors 252 and 254 is completed when SCR 238 is turned on. A pilot lamp 256 is shunted from the anode of battery 244 to that of SCR 238 to indicate when the SCR is on to complete the power circuit of UJT 250.

In order to turn on the UJT after its power circuit is completed, the emitter or control electrode thereof is connected to the adjustable tap of a potentiometer 258 which in turn is connected through resistors 260 and 246 to the anode of battery 244. The resistors 246 and 260 and the potentiometer 258 cooperate with a capacitor 262 to form an RC timing network connected across the battery 244 whenever SCR 238 is turned on. This timing network measures out a timing interval, starting with the turning on of SCR 238 and tenninating whenthe capacitor 262 is sufficiently charged to trigger the emitter of the UJT 250. At that point the UJT turns on, discharging the timint capacitor 262. A Zener diode 264 is connected across the potentiometer 258 and capacitor 262 for voltage regulation purposes, to provide timing accuracy despite changes in the voltage supplied by battery 244.

When UJT 250 turns on, ending the measured delay interval of the circuit 116, the UJT load current develops an output across resistor 254, which is applied over leads 117 and 270 to the input of the trigger switch circuit 114. The latter circuit is then caused to switch a low power relay comprising a solenoid 272 and three normally opened switches 274 which are in series with the three phase circuit from generator 100 to the triac circuit 106. Thus, a switching operation which is conducted at relatively low power levels in the trigger switch circuit 114 controls the switching of a high power output by the triac circuit 106.

The input arriving over leads 1 17 and 270 is applied to an RF filter comprising a shunt resistance 276 and capacitance 278. The filter output is applied through a current limiting resistor 280 to the gate-cathode circuit of an SCR 232 which is connected in series with the relay coil 272, a normally closed, relay-opened switch 284, a normally closed, manually opened switch 286 and a battery or other DC source 288. The input from delay circuit 110 turns on the SCR 282 and thus allows the battery 288 to energize the relay coil 272, closing the relay switches 274. A diode 290 is shunted across the relay coil 272 for dropping transients, and a pilot lamp 292 is also connected across the relay coil to indicate when the relay is on.

The three phase input applied over lines 108 is coupled through respective shunted transformers 300. One side of each transformer primary is returned to ground, which is the potential of the center point of the Y-connected generator 100. The transformer secondaries are connected through the respective relay-controlled switches 274 to respective RF filters comprising shunt resistances 302, shunt capacitors 304 and series resistances 306. The filter output is connected to respective triacs 308, one for each of the three phases. The outputs of the triacs are connected over respective leads 103 to the Variac circuit 107 and the three phase input of the linear actuators 104. Respective double diodes 310 are shunted across the triac inputs for bidirectional voltage regulation.

In FIG. 3 the linear actuators 104 are shown in greater detail as a pair of devices 104.1 and 104.2, each of which comprises a delta-connected three phase stator coil assembly 400 having input terminals 402, 403 and 404. The stator coils 400, when suitably energized by a polyphase input, produce a moving magnetic field which sweeps linearly along the stator coil assembly. This moving magnetic field is followed by linear motion of an armature 406, and is synchronous with the 60 cycle input to the stator coil assembly 400.

The electrical contacts 102 are mounted on the ends of respective insulated holders 408 which travel with armatures 406 of the synchronous linear actuators 104.1 and 104.2. In order to draw an are between contacts 102 by breaking the circuit, the armatures 406 are driven apart as indicated by arrows 410. They can also be driven together to close the contacts 102.

The direction of motion of each armature 406 is controlled by the phase relationships at the stator input terminals 402, 403 and 404. Thus, in order to achieve contact-breaking, the circuit connection of FIG. 4 is employed. There it is seen that the three phase actuator input lines 105 are connected to the stator coil assemblies 400 of the two linear actuators 104.1 and 104.2 in

such a way that the corresponding stator input terminals 403 of the two actuators are connected to the same phase of the three phase input line 105, but the stator input terminals 402 and 404 thereof are reversed for connection to different phases. This causes the armature 406 of the linear actuator 104.1 to move to the left and that of the linear actuator 104.2 to move to the right as indicated by arrows 410 in FIG. 3, for the purpose of separating the arcing contacts 102.

The linear actuators 104 may be of a type which is commercially available under the trademark Polynoid from Skinner Precision Industries, Inc. of New Britain, Conn. The advantage of using this type of actuator in the arc testing device of this invention is that it combines a long and linear armature stroke with synchronous speed, the latter feature assisting in the precise and repeatable timing of the are relative to electrical phase angle. The delay caused by the necessity for first accelerating the armatures 406 to synchronous speed and then driving synchronously through the remainder of a test stroke, is of course accurately compensated by the proper setting of the potentiometer 258 to tune the time delay circuit 116, and of the potentiometer 220 to select the initial electrical phase angle sensed by the circuit 112.

The circuitry so far described is designed to energize triac circuit 106, and thus to start the actuators 104, at a time precisely related to the phase angle of the arc source generator 100. Once the actuators 104 begin moving, the delay until arc inception occurs depends on the initial positions of the actuators, the level of acceleration imparted to them while they are building up to synchronous speed, and, if synchronous speed is attained prior to are inception, the synchronous speed level. For a given linear actuator, the acceleration is a function of the actuator drive voltage on lines 105; thus the setting of the Variac control 107 can be used to affect the time delay between triac triggering and arc inception. The synchronous speed is of course a function of the frequency of the actuator drive source (generator in this instance), and thus it is fixed in the usual test situation where 60 cycles or some other standard power frequency is employed. It follows that the time of arc inception can be controlled as a function of the phase angle of source 100, so far as it is possible to do so, by proper adjustment of phase sensing circuit 112, time delay circuit 116, and Variac circuit 107. Other factors which also have a slight effect on the precise moment of arc inception, such as dirt, humidity, atmospheric composition, etc., are not readily amenable to control.

Arc duration is the time interval from are inception until the moving contacts 102 either mate or move too far away to sustain an arc (depending on the direction of movement). For a given linear actuator, the length of this interval again depends on the acceleration imparted to the actuators 104 from are inception until synchronous speed is reached, and on the synchronous speed thereafter. Thus, for a given test frequency, the arc duration is controlled by adjusting Variac circuit 107 within the range of settings which delay the attainment of synchronous speed until some time after arc inception.

The linear actuators preferred for use with this arc tester are subject to stator coil bum-out if they are left 7 on for too long a time. Accordingly, there is provided a protective circuit, illustrated in FIG. 5, the function of which is to turn the circuit of FIGS. 1 and 2 on and off at the proper times to prevent burning out of the stator coils 400.

This circuit draws 60 cycle single phase power from a line 500 which is connected through a manual on-off switch 502 to the primary of an isolating transformer 504. The transformer secondary is connected to a halfwave rectifying diode 506 and a filtering network comprising a resistance 508 and capacitor 510. The capacitor voltage is applied through a normally open, manually closed start switch 512 to a relay coil 514 which is in series with a normally closed, relay-opened switch 516. Upon manual closure of the start switch 512, the relay coil 514 is energized to close relay switches 518, 520 and 522. Switch 518 is a holding switch which shunts the manual start switch 512 to keep the relay coil 514 energized after the manual switch is released. Switch 522 provides an oscilloscope signal to that the start of the testing operation can be visually displayed.

The switch 520 applies power to an RC timing network comprising a resistor 524 shunted by a potentiometer 526 and connected across the timing capacitor 528, and at the end of the charging interval of the timing capacitor 528 the capacitor voltage is high enough to cause relay coil 530 to close a pair of normally open relay switches 230 and 532. The switch 230, seen also in FIG. 2, connects the output of the phase sensor circuit 112 to the input of the tuneable time delay circuit 116. It is only after the switch 230 is thus closed by the relay coil 530 that the circuits 116, 114 and 106 can respond to the next phase-sensing event of the circuit 112. Thus, the are testing operation can only begin at the endof the time interval measured by the capacitor 528. Potentiometer 526 is used to adjust the time interval.

The other switch 532 closed by the relay coil 530 energizes another RC timing network comprising a resistor 534 shunted by a potentiometer 536 and a capacitor 538. After the lapse of a time interval required for charging the timing capacitor 538, a relay coil 540 connected across the capacitor becomes sufficiently energized to open normally closed relay switches 240, 284 and 516. Relay switches 240 and 284, seen also in FIG. 2, turn off the turnable time delay circuit 116 and the trigger switch 114 by extinguishing SCRs 238 and 282 respectively. Thus the termination of the timing cycle of capacitor 538 disables circuits 116 and 114, to terminate energization of the relay coil 272 and open the relay switches 274. This in tum disables the triac circuit 106 at the end of the prescribed interval, to prevent further energization and possible burn-out of the linear actuator stator coils 400. 1 The other relay-operated switch 516 de-energizes the first relay coil 514 and thus releases its holding It will therefore be appreciated that this device is capable of closing or opening a pair of high voltage contacts to strike an arc across an AC generator at any desired phase angle thereof, as determined by a phase sensing circuit and a tuneable time delay circuit responsive thereto, and to maintain the are for a desired interval. In addition, there is circuitry following the tuneable time delay which switches a relay at low power intervals to control higher power levels used to drive synchronous linear actuators for the purpose of transferring the arcing contacts. Finally a protective circuit is provided which times the operation of the arc tester circuitry and prevents burning out of the actuaswitch 518. Switch 516 also makes a circuit through a tor coils.

Since the foregoing description and drawings are merely illustrative, the scope of the protection of the invention has been more broadly stated in the following claims; and these should be liberally interpreted so as to obtain the benefit of all equivalents to which the invention is fairly entitled.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as fol lows:

1. An are testing device comprising:

AC power input means;

a pair of switchable electrical contacts connected across said power input means to create an are upon switching;

electro-mechanical actuator means for switching said contacts;

a timing circuit responsive to a selected phase angle of the power input to energize said actuator means for switching said contacts whereby said are occurs in predetermined phase relationship to said power input; a protective circuit for issuing a start signal, measuring a predetermined safe interval, and then automatically issuing a stop signal at the end of said safe interval;

and means for enabling said timing circuit upon receipt of said start signal and disabling said timing circuit upon receipt of said stop signal.

2. A device as in claim 1 wherein:

said actuator means comprises at least one synchronous linear actuator including a coil assembly for producing a magnetic field which moves over a linear path in synchronism with said AC power input and an armature responsive to said magnetic field over said linear path thereof;

said actuator coil assembly comprises a plural phase input;

said timing circuit comprises a plural phase output connected to said plural phase input;

said armature is connected to transport one of said electrical contacts for switching purposes whereby to create said arc;

and further comprising:

a second plural phase input synchronous linear actuator having an armature arranged to transport the other of said electrical contacts;

said plural phase output stage being connected to the input of said linear actuator in a reverse sense relative to said first-mentioned linear actuator, whereby said actuators transport their respective electrical contacts in opposite directions to cooperate in switching said contacts.

3. A device as in claim 1 further comprising:

means responsive to said timing circuit to adjust the level of energization of said actuator means; said actuator means varying the acceleration imparted to said contacts as a function of said energization level. 

1. An arc testing device comprising: AC power input means; a pair of switchable electrical contacts connected across said power input means to create an arc upon switching; electro-mechanical actuator means for switching said contacts; a timing circuit responsive to a selected phase angle of the power input to energize said actuator means for switching said contacts whereby said arc occurs in predetermined phase relationship to said power input; a protective circuit for issuing a start signal, measuring a predetermined safe interval, and then automatically issuing a stop signal at the end of said safe interval; and means for enabling said timing circuit upon receipt of said start signal and disabling said timing circuit upon receipt of said stop signal.
 2. A device as in claim 1 wherein: said actuator means comprises at least one synchronous linear actuator including a coil assembly for producing a magnetic field which moves over a linear path in synchronism with said AC power input and an armature responsive to said magnetic field over said linear path thereof; said actuator coil assembly comprises a plural phase input; said timing circuit comprises a plural phase output connected to said plural phase input; said armature is connected to transport one of said electrical contacts for switching purposes whereby to create said arc; and further comprising: a second plural phase input synchronous linear actuator having an armature arranged to transport the other of said electrical contacts; said plural phase output stage being connected to the input of said linear actuator in a reverse sense relative to said first-mentioned linear actuator, whereby said actuators transport their respective electrical contacts in opposite directions to cooperate in switching said contacts.
 3. A device as in claim 1 further comprising: means responsive to said timing circuit to adjust the level of energization of said actuator means; said actuator means varying the acceleration imparted to said contacts as a function of said energization level. 